Method and apparatus for continuous electrolytic polishing of fine metal wires

ABSTRACT

IN AN APPARATUS FOR EFFECTING THE CONTINUOUS ELECTROLYTIC POLISHING OF FINE METAL WIRES AN ELONGATED ELECTROLYTIC CELL IS DIVIDED INTO A PLURALITY OF ELECTROLYTIC CHAMBERS BY MEANS OF A PLURALITY OF PARTITION WALLS HAVING ALIGNED LIMITED OPENINGS TO PASS A STRAIGHT WIRE. AN ELECTROLYTE HAVING LOWER RESISTANCE THAN THE WIRE IS CIRCULATED THROUGH THE CELL SUCCESSIVELY THROUGH THE LIMITED OPENINGS AND CHAMBERS AND ALTERNATING CURRENT IS PASSED THROUGH THE WIRE WHEREBY IN EACH CHAMBER THE CURRENT FLOWS MAINLY THROUGH THE ELECTROLYTE TO CREATE POLARIZATION. THE APPARATUS IS UTILIZED IN A CONTINUOUS WIRE FINISHING LINE.

Dec. 28, 1971 yos mu ETAL 3,630,864

METHOD AND APPARATUS FOR CONTINUOUS ELECTROLYTIC POLISHING 0E FINE METALWIRES Filed June 13, 1968 FIG.

FIG. 3

United States Patent 3,630,864 METHOD AND APPARATUS FOR CONTINUOUSgvLEgTROLYTlC POLISHING OF FINE METAL IR S Kiyoshi Nakamura, Chiba-shi,Koji Nabae, Yokohamashi, and Nobuo Ohsawa, Kawasaki-shi, Japan,assignors to Tokyo Shibaura Denlri Kabushilri Kaisha, Kawasakishi, JapanFiled June 13, 1968, Ser. No. 736,700 Claims priority, applicationJapan, June 19, 1967, 42/38,889; Sept. 13, 1967, 42/77,837 Int. Cl.C2310 3/06; Btlllr 3/00 US. Cl. 204140.5 3 Claims ABSTRACT OF THEDISCLOSURE BACKGROUND OF THE INVENTION This invention relates to amethod and apparatus for continuous electrolytic polishing of fine metalwires.

Continuous electrolytic polishing has been carried out by passing a finemetal wire through one or a plurality of spaced apart rectangular boxshaped electrolytic cells Electric current was passed through the wireby means of a contact means outside the cell consisting of a mercuryterminal, metal wool, a metal roller of the like and a counter electrodein the cell, or contact means of the type referred to above provided onthe opposite ends of the metal wire outside the cell, or contact meanson the opposite ends of the metal wire outside the cell and a counterelectrode in the cell or two electrodes immersed in separateelectrolytic cells. The fine wire to be treated was passed through anelectrolyte by means of guide rollers or passed linearly in theelectrolyte through small notches or slots, passed between an outsidecontact and a contact disposed in the cell along a spiral or a pluralityof parallel go and return paths. Further direct current has beenexclusively used to perform electrolytic polishing. However, in one typeof prior method wherein the wire is caused to run linearly-and currentis passed through the wire by means of an outside contact and anelectrode disposed in a cell, when treating very fine wires havingdiameters of less than 0.02 mm., for example, the electrical resistanceof the wire itself becomes so high that no additional advantage could beexpected by increasing the length of the cell or the length of the wireimmersed in the electrolyte. In such a case, satisfactory electrolysiscould not be realized unless the running speed of the wire was greatlyreduced or unless a number of electrolytic cells were employed. Where anumber of cells are arranged in cascade, the number of contacts to beinstalled outside the cells increase whereby the resistance to thepassage of the wire is increased thus making it difiicult to increasethe running speed of the wire. Installation of a number of cells alsoincreases the cost of installation.

With the arrangement wherein a plurality of electrolytic cells arearranged in cascade and wherein a voltage is applied to the wire acrossoutside contacts on the opposite ends thereof, all of the electriccurrent supplied between the outside contacts and cells and betweendifferent cells flow through the fine metal wire being treated, so thatit is impossible to use current of the value exceeding the permissiblemelting current of the wire. Unfortunately unless the electrolysiscurrent is limited to about 50% of the permissible current for the finewire being treated, the wire is heated to oxidize its surface during theperiod when it is running in air outside the electrolyte. For thisreason, the running speed of the Wire is limited by the number of cellsinvolved. Generally, in order to perform electrolytic treatment atspeeds higher than 30 m./min., it is necessary to use a great manycells.

Furthermore, in the arrangement wherein the wire is repeatedly passedbetween an external contact and an electrolytic cell, the wire to betreated is liable to be subjected to a high tension, so that unlessthick wires having considerably high breaking strength is utilized, itis impossible to increase the running speed of the wires. Treatment offine wires whose mechanical characteristics tend to vary involves manyproblems.

In the manufacture of fine wires of tungsten or molybdenum which areutilized to manufacture incandescent lamps or electronic tubes, thedrawn wires must be finished through a number of steps including a curlremoving step in which the curl of wires caused by residual strain whichwas imparted to the wires when they are reduced through wire drawingdies, a step of electrolytic polishing in which oxides or lubricant suchas fine particles of graphite utilized in the wire drawing dies isremoved, a step of washing wires after electrolytic polishing, and astep of continuously measuring the diameter of wires.

It is of course desirable to perform these steps in one continuousprocessing line at a high speed. Among these various steps, the step ofelectrolytic polishing is most important because the running speed ofthe wire through the processing line is essentially determined by thespeed at which the Wire can pass through the electrolytic polishingdevice without the accompanying troubles mentioned above.

SUMMARY OF THE INVENTION Accordingly it is an object of this inventionto provide a new and improved method and apparatus for electrolyticallypolishing metal wires and which is capable of polishing or cleaning finemetal wires at high speeds.

Another object of this invention is to provide an improved continuousfinishing apparatus for fine metal wires.

Briefly stated, according to this invention, an elongated electrolyticcell is divided into a plurality of electrolytic chambers by means of aplurality of spaced apart partition walls which are provided withaligned limited openings to linearly pass therethrough a wire and anelectrolyte. The electrolyte has a resistance lower than that of thewire and is circulated through the electrolytic cell successivelythrough limited openings and electrolytic chambers.

A pair of electrodes are provided in the electrolytic chambers at theopposite ends of the cell to pass alternating current through the wire.As the electrolyte in each chamber has a much lower resistance than thewire, most of the current fiows through the electrolyte in eachelectrolytic chamber whereby a polarization phenomenon is created toelectrolytically polish the surface of the wire. The invention isespecially suitable for treating fine wires of tungsten or molybdenumhaving diameters ranging from 0.005 to 0.1 mm.

For these applications, the electrolyte advantageously consists of 1 to30% solution of caustic soda.

As the novel electrolytic polishing apparatus permits high speed runningof the wire being treated without any appreciable friction, it issuitable for use in a continuous metal wire finishing line includingmeans to eliminate curl, an electrolytic polishing apparatus, a washingdevice and means to continuously measure the diameter of the wire whichare arranged in the order mentioned.

BRIEF DESCRIPTION OF THE DRAWING tially all the current flows throughthe wire while it is passing through the notch. However, in eachelectrolytic chamber, current flows through the electrolyte in parallelwith the wire as indicated by arrows in FIGS. 2A and 2B. FIG. 2A showsthe flow of current during a positive half This invention can be morefully understood fr m th cycle while FIG. 2B shows that during anegative half following description taken in connection with theaccycle. companying drawing in which: Taking a tungsten wire as anexample, the resistivity FIG. 1. shows a perspective view of anelectrolytic cell of tungsten is about 5.5 micro ohm-cm. and theresistance utilized to carr out this invention; 10 of a tungsten wire of13 micron diameter and 10 cm. FIGS. 2A and 2B are plan views of theelectrolytic cell length is about 42 ohms. On the other hand theresistivity shown in FIG. 1 useful to explain the operation of th s ofcaustic soda solution is about 5 ohm-cm. but since invention, and thecross-section of the electrolyte in each electrolytic FIG. 3 is adiagrammatic repres ntation of a C tiH chamber is much larger than thatof tungsten wire, the ous wire finishing line employing the novelelectrolytic 15 resistance of the electrolyte is very small.Accordingly, in cell. the electrolytic chamber most of the current flowsthrough DESCRIPTION OF THE PREFERRED the electrolyte. During thepositive half cycle, current EMBODIMENT flows as shown in FIG. 2A. Atportions a near one end Referring now to the accompanying drawing, theelec of the chamber where current flows into the electrolyte trolyticapparatus 1 shown in FIG. 1 comprises an elon- 29 F the tungsten, W1rear l oxldlzl ng rfaacnon correspond gated electrolytic cell or tank 2 ofa suitable electric inmg to the electric quantlly ,fiowmg IntoElectrolyte sulating material such as hard vinyl resin, a pay-out reelconvert .tungsten Into tungsten Oxide (W93) 3 and a take-up reel 4 onthe opposite sides of the cell. As 15 then dlsolved m the olyte 9forfflfotasslum shown, the cell is divided into a plurality of chambersor tungstate dlssolvable therem' At Pomons near the compartments 7a, 771) by means of a plurality of 2; other end of the chamber where currentreturns to the equally spaced parallel partition walls 6 having axiallytungsten hydrogel, F h the metal aligned small notches or slots 5 at theupper center theresurfac? exposed at Pomons a by dlssolvmg the Surfaceof. Both side edges and the bottom edge of each partition layer furtherChang] the eYolved hydrogen Dumlg wall 5 are liquid-tightly orfluid-tightly secured to side 9 neganve half cycles simllar reactlonsprfmeed as shown In Walls and a bottom wall respectively, of the Cell todefine .10 FIG. 2B. These reactions are repeated in successive elecaplurality of independent electrolytic Chambers 7 a troyltlc chambers topollsh and clean the fine metal wire. 71) 711 which are electricallyisolated from each other h dlameter of the Wire Increases the reslstance of the except through the narrow passages comprising the wiretself decreases so that current flows mainly through notches 5. A pairof electrodes 8a and 812 made of stainless h wlre thus reducmg thepollshmg effect by the Polanza' sheet, for example, are disposed in theendmost electrotion phenomena lytic chambers 70 and 7/1 on both ends ofthe cell 2. The t hls manner accordmg to thls electFolytlc electrodesare electrically connected to a source of alterfine metal W1res can R Bovlded Wlth an nating current 10 via an adjustable resistor Accordingelectrolytic cell of a speclal construct1on 1n the same manto thisinvention, it is important to use an electrolyte hav- 40 as If a numberof Spaced apart Cells were arranged ing an electric resistance lowerthan that of the fine wire Cascade- 11 being treated. Thus for example,when it is desired to Following Table 1 shows various parametersutilized treat a tungsten or molybdenum wire having a diameter of inthree examples.

Table 1 Cone. of Diameter of Diameter of caustic AC untreated finishedsoda, Speed Example Material wire, mm. wire,mm. percent Volt. Amp m/min1 Tungsten 0. 014 0.011 2 15 1.5 100 2 -do 0. 032 0. 027 2 13 2. 0 3Molybdenum 0.104 0. 004 5 12 10.0 30

from 0.005 to 0.100 mm., 1 to 30% solution of caustic After electrolytictreatment, the surface of each wire soda is preferred. The electrolyteis serially circulated was extremely clean, smooth and brilliant.through successive electrolytic chambers from a tank 12 A describedabove, in fine wire of tungsten and connected to the bottom ofelectrolytic chambers 7a and molybdenum ar d wn throu h di at hightemperatures, 712 at the opposite ends via a pump 13. Alternatively, thetheir surfaces are covered by layers of graphite which was electrolytecan be supplied to chamber 7a from above. utilized as the lubricant oroxides. However, these layers In operation, the fine metal wire 11 iscaused to travel can be effectively removed by hydrogen gas evolved atfrom reel 3 to reel 4 through the small slots or notches 5 portions [1acting as cathodes. This cathodic cleaning of respective partition walls6 and through the electrolyte action further improves the efliciency ofthe anodic eleccontained in the cell 2. trolytic polishing actionettected at portions a.

Concurrently therewith, a suitable AC voltage is ap- While the novelmethod is particularly effective for plied across electrodes 8a and 8bto cause electrolytic fine wires of the diameter of from 0.005 to 0.100mm., polishing. FIGS. 2A and 2B diagrammatically illustrate the resultof experimentation showed that the invention the polarization phenomenaoccurring at this time. Where can be applicable to wires having largerdiameters. By the resistance of the electrolyte is considerably higherthe selection of a suitable electrolyte, nearly all metals than that ofthe wire being treated, substantially all curcan be treated according tothis invention. rent fiows through the wire thus causing no electrolyticSince alternating current is utilized to carry out the action. However,where the resistance of the electrolyte novel method of continuouselectrolytic polishing of fine is lower than that of the wire (e.g.where the diameter metal wires, the polishing efficiency can beimproved, with of the wire is smaller than 0.15 mm.), a substantialporlarge reduction in diameter or large quantity of removal tion of thecurrent flows through the electrolyte contained by electrolyticpolishing. Further, the fioor space can be in each chamber as shown inFIG. 2. More particularly, saved because a number of. spaced apart cellsare not since the cross section of the notch 5 is small, substanused asin the prior arrangement.

In addition, as the wire being treated is always kept immersed in theelectrolyte, it is etfectively cooled by the electrolyte with the resultthat more current can be passed therethrough, thus increasing thecurrent density. The surface condition or flatness of the treated wireis excellent and the surface is brilliant. Very fine wires of less than0.020 mm. diameter can be passed through the electrolytic cell at a veryhigh speed of the order of 100 m./ min. Linear running of the Wire doesnot alter the mechanical characteristics thereof before and aftertreatment. Use of alternating current eliminates the need of a rectifierdevice, thus reducing the cost of installation.

FIG. 3 illustrates a continuous finishing line including the novelelectrolytic polishing apparatus 20.

As shown, a fine wire 21 to be treated is payed out from a pay-out reel22 connected to a split phase start type motor 23 which functions toapply a predetermined back tension to the wire. After passing through aguide roller 24, the wire enters into a curl eliminating device 26including an electric heater 28 which is energized by a regulatingtransformer 27 to maintain the temperature of the wire in a range offrom 500 to 700 C., for example, which is required to remove curl. Wherethe wire is in the as-drawn state, curl removal may be effected in theopen air but in some cases it is advantageous to perform this operationin a reducing or inert atmosphere.

The straightened wire is then passed through the electrolytic polishingdevice 20 embodying this invention and comprising an electrolitic cell29 divided into a plurality of chambers 31 by partition walls 30including slots (not shown) similar to slots shown in FIG. 1. Electrodes25a and 25b immersed in end chambers are energized by a source ofalternating current 10. The wire is then washed by a washing device 32to remove remaining alkaline electrolyte and then passed through a hotair drier 33. The wire 21 is then passed through a continuous diametermeasuring device 34 and is finally wrapped around a takeup reel 40.

Diameter measuring device 34 includes a pair of mercury cups 35containing mercury to pass current through the wire to continuouslymeasure the electrical resistance thereof. The measured resistance isindicated by an indicator (not shown) in terms of the diameter. Betweendiameter measuring apparatus 34 and the take-up reel 40 are provided alength measuring device 36 with a suitable length meter and a guideroller 37. The take-up reel may comprise an auxiliary reel upon whichthe wire is to be wrapped during the starting or accelerating period anda main reel upon which the wire is to be wrapped after it has beenaccelerated to a predetermined constant speed.

Table 2 shows comparison of running speed of the novel device and aconventional finishing device.

Increase in the running speed by about three times is due mainly tolinear movement of the wire and substantially no contact resistance atthe contacts for supplying current thereto. It is evident that such acontinuous finishing line greatly saves the labor and time when comparedwith the prior arrangement wherein various process steps are carried outindependently and non-continuously.

While the invention has been described in terms of preferred embodimentsit will be clear that various changes and modifications may be madewithout departing from the true spirit and scope of the invention asdefined in the appended claims.

What is claimed is:

1. A method of continuously electrolytically polishing metallic wirecomprising: providing a metallic wire to be polished; provided aplurality of serially spaced-apart compartments each containing thereinan electrolytic solution having an electrical resistance within eachcompartment less than the electrical resistance of the metallic wire andwherein only each endmost compartment contains therein an electrode;serially circulating said electrolytic solution through saidcompartments; longitudinally advancing said metallic wire successivelythrough said compartments in the direction of circulation of saidelectrolytic solution; and applying an alternating electric current tosaid electrodes effective to create alternating electrical polarizationzones within the electrolytic solution contained in each saidcompartment except said endmost compartments during the longitudinaladvancement of said metallic wire to effect electrolytic polishing ofthe metallic wire.

2. A method according to claim 1; wherein said metallic wire has adiameter of from 0.005 mm. to 0.1 mm. and wherein said electrolyticsolution comprises a 1 to 30% solution of caustic soda.

3. Apparatus for continuously electrolytically cleaning metallic strandscomprising: means defining a plurality of. fluidtight compartmentssuccessfully spaced-apart along a longitudinal axis receptive during useof the apparatus of an electrolytic solution, each compartment havingmeans therein defining strand openings all of which are positioned inalignment along said longitudinal axis; advancing means forlongitudinally advancing a metallic strand to be cleaned through saidstrand openings; circulating means including said strand openings forcirculating the electrolytic solution serially through saidcompartments; and alternating current means comprising a pair ofelectrodes each disposed within an end one of said plurality ofcompartments as viewed along said longitudinal axis, the intermediatecompartments being free of electrodes, and an alternating electriccurrent source connected to said pair of electrodes coacting with saidelectrolytic solution and the metallic strand for establishing in eachof said compartments except said end ones-an alternating current flowaccompanied by the creation of correspondingly alternating polarizationzones to effect electrolytic cleaning of the metallic strand; andwherein each said compartment has opposed side wall portions disposed inspaced-apart relationship along said longitu dinal axis, wherein saidstrand openings comprise means defining a slot in the upper portion ofeach side wall portion dimensioned to concurrently receive therethroughboth the metallic strand and the circulating electrolytic solution, andwherein the cross-sectional area of said slots is dimensionedsufficiently smaller than the cross-sectional area of said compartmentsto ensure that the current flow within each compartment occurs primarilywithin said electrolytic solution while the current flow between eachsaid compartment within the region of said slots occurs primarily withinthe metallic strand.

References Cited UNITED STATES PATENTS 3,287,238 11/1966 Latawiec et al204-140.5 3,338,809 8/1967 Stricker 204- JOHN H. MACK, Primary ExaminerN. A. KAPLAN, Assistant Examiner US. Cl. XrR.

